[Huntress]

Norman is just the unfortunate victim of a blocked urinary tract, which according to my vet is a very common problem in tom cats. In his case, the blockage was so bad that the only cure was a perineal urethrostomy—essentially a kitty sex change. Norman’s still 100% male in his little cat brain; he just doesn’t have male equipment any more.

[NewJerseyJoe]

That makes sense. I would guess that calling it "transsexual" surgery probably helps to lighten the mood of what is a serious surgery -- kind of like people in the hospital laughing at their serious medical issues, so as not to make it into a spectre that ruins their outlook.

If there were veterinarians performing real "transsexual" mutilations on animals -- helping with their "gender identities".... now that's just too creepy a thought....